We are studying the control of fibrinogen gene expression as a model for investigating the mechanisms of coordinate gene expression. We have found the levels of fibrinogen mRNA rapidly increase after defibrinating rats with Malayan pit viper venom. During this response each of the three fibrinogen mRNA's increase at the same time, rate and to nearly the same extent; thus their expression is highly coordinated. We have constructed cDNA and genomic clones for each of the fibrinogen genes and are analyzing structural similarities between the genes which might account for their coordinate regulation. We have also begun cloning the human fibrinogen genes and plan to study the human afibrinogenemias as a model of the effects of mutation on gene expression.